SAT Writing Practice 1 + Answer and Explanation

SAT Writing Practice 1

The answer is in the first comment below.↓

grateful, gratitude, gratuitous, and gratuity

grateful, gratitude, gratuitous, and gratuity 

Grateful = thankful

Gratitude = thankfulness

Gratuitous = free; unnecessary, uncalled for

Gratuity = tip given to a waiter, valet, etc. 

censor, sensor, censure, and censer

censor, sensor, censure, and censer